1. Field of the Invention
The present disclosure relates to an inkjet recording head which carries out recording by ejecting ink.
2. Description of the Related Art
Recently, inkjet recording apparatus, which was typically intended for home use, has been applied to a wide variety of fields; inkjet recording apparatus is used in offices or for retail photographing in the business field and used for drawing electronic circuits and manufacturing flat panel displays in the industrial field. In this trend, there is a demand that the inkjet recording apparatus has an increasingly higher recording speed. Some measures have been taken to meet the demand: for example, increasing driving frequency of an energy generating element used for the ejection of ink, and employing a linear head of which width of the inkjet recording head (hereinafter, “head”) is longer than the width of a recording medium.
However, if driving frequency of the energy generating element is increased to meet the demand for a higher speed, density of power supplied to the head becomes high. Especially in an ejection system in which the ink is heated and made to boil and then ejected using the bubble generating energy, an increase in power density causes a greater increase in temperature of the head and, as a result, affects image quality. This is because an increase in head temperature causes an increase in ink temperature, and the increased ink temperature causes a fluctuation in the amount of the ink to be ejected; and therefore, recording density varies between the beginning of recording and the rest of time during the recording. In an ejection system in which a piezoelectric element is used, an increase in ink temperature caused by the ejection of the ink is not significant and, therefore, an influence on image quality by the increased density of supplied power is relatively small. The ejection system in which a piezoelectric element is used has the following problem. If the ink is ejected using shear strain (i.e., shear mode) of the piezoelectric element, energy efficiency for the ejection is low and an increase in ink temperature is large; therefore, image quality is easily affected.
Besides the influence on image quality caused by the increase in head temperature, distribution of temperature along a longitudinal direction of the recording element substrate may cause varied density in an image along the longitudinal direction of the recording element substrate. This is because heat tends to accumulate at the central portion and tends to be lost at end portions along the longitudinal direction of the recording element substrate.
Japanese Patent Laid-Open No. 2007-168112 proposes, as illustrated in FIG. 7 thereof, a configuration to address the above-described problem. In the proposed configuration, a coolant flow channel is provided such that a coolant flow channel (in particular, liquid cooling pipes 15 and 16) as the coolant flow channel overlaps the central portion of a recording element substrate along a direction vertical to an ejection port surface of the recording element substrate.
However, it is still difficult by the configuration described in Japanese Patent Laid-Open No. 2007-168112 to sufficiently reduce difference in temperature between the central portion and the end portions along the longitudinal direction of the recording element substrate. Especially during high-speed recording, the amount of heat generated in each recording element substrate is large and therefore the problem regarding the difference in temperature of the recording element substrate becomes noticeable.